Nurse Gicela Buenrostro prepares flu vaccinations for patients at the Kaiser Permanente injection clinic in Redwood City, Calif. on Friday, Dec. 27, 2013. A recent uptick in reported cases of influenza indicates the flu season is in full swing.

Photo: Paul Chinn, The Chronicle

Nurse Gicela Buenrostro prepares flu vaccinations for patients at...

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Jocelin Hernandez, 12, is vaccinated against the flu by Alheli Hocker, a nurse at the Kaiser Permanente injection clinic in Redwood City, Calif. on Friday, Dec. 27, 2013. A recent uptick in reported cases of influenza indicates the flu season is in full swing.

Photo: Paul Chinn, The Chronicle

Jocelin Hernandez, 12, is vaccinated against the flu by Alheli...

Image 3 of 5

Information on current flu vaccinations is distributed to patients at the Kaiser Permanente injection clinic in Redwood City, Calif. on Friday, Dec. 27, 2013. A recent uptick in reported cases of influenza indicates the flu season is in full swing.

Photo: Paul Chinn, The Chronicle

Information on current flu vaccinations is distributed to patients...

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Meichen Wang comforts her 3-year-old daughter Mia Lin while nurse Alheli Hocker prepares Mia for a flu vaccination at the Kaiser Permanente injection clinic in Redwood City, Calif. on Friday, Dec. 27, 2013. A recent uptick in reported cases of influenza indicates the flu season is in full swing.

Photo: Paul Chinn, The Chronicle

Meichen Wang comforts her 3-year-old daughter Mia Lin while nurse...

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Samantha Torrestower (right), 14, gets vaccinated against the flu by nurse Aheli Hocker while Samantha's brother Connor, 10, has his sleeve adjusted by their mother, April Torres (upper left), after his shot at the Kaiser Permanente injection clinic in Redwood City, Calif. on Friday, Dec. 27, 2013. A recent uptick in reported cases of influenza indicates the flu season is in full swing.

Health officials are attributing five more deaths to a virulent strain of influenza that is making its way across the Bay Area.

The death of a non-elderly man in San Francisco marks the city's second death of the season. Officials with the Department of Public Health confirmed late Tuesday that the death was related to influenza, but said that it would take a few days to determine the strain.

In Contra Costa County, three more deaths were said to have been caused by the flu. Two men died, one in his 30s and another in his 50s, along with a woman in her 60s.

San Mateo County health officials also confirmed another flu-related death, adding to the three that had already been reported.

This strain of influenza has claimed the lives of six people in Santa Clara County, four each in Sonoma and San Mateo counties, three in Alameda County, two in Marin and one in Solano County.

Across the region, 27 deaths had been attributed to the flu as of Wednesday.

The strain of influenza that has taken hold this year seems to be targeting younger and healthier people, though the majority of recent victims had underlying health conditions. Many of the victims were in their 30s and 40s and the youngest victim, Matthew Walker of Santa Rosa, was 23.

Authorities said the only way to completely protect yourself is to receive a vaccination.

The vaccine is well-matched to this year's flu season and protects against all strains of influenza that have been identified in patients. The primary strain circulating this year is Type A, subtype H1N1 - also known as the "swine flu," which caused a global outbreak in 2009.

The flu vaccine takes about two weeks to become fully effective, so public health experts recommend people get it now if they haven't already. To get the vaccine, call your health care provider, or go to http://flushot.healthmap.org to find the nearest supplier.